The present invention relates to intrusion detection systems, and particularly to the taut wire type system which produces an electrical signal when a sensor wire is cut or disturbed.
Taut wire intrusion detection systems are now commonly used in security fences to detect an attempt to penetrate through or over the fence. However, the known systems do not detect an attempt to penetrate under the fence, e.g. by digging a tunnel, and therefore in high security places a barrier, such as a concrete wall, may have to be built under the ground below the fence to prevent such an attempted penetration. In addition, the known security fences usually do not detect the presence of a person near the fence, but rather detect his presence only when actual contact is made with the fence, e.g., by cutting or moving one of the sensor wires.
An object of the present invention is to provide an intrusion detection system having advantages in one or more of the foregoing respects. Another object of the invention is to provide an intrusion detection system particularly useful with security fences but which may also be used apart from security fences, to detect an attempted tunnelling into a protected area, or to detect the presence of a person near or in a protected area.